Bedrest is used prophylactically by 92% of obstetricians to treat 18.2% of the 4 million women who become pregnant each year. It is used in an effort to reduce the incidence of low birth weight. Numerous adverse effects of bedrest have been documented in nonpregnant populations. Physicians, however, have not applied this knowledge to the care of pregnant women. A common attitude is that the physiology of pregnancy is different and thus bedrest is either not harmful to young healthy women or is a small price to pay for a viable infant. Yet, the high costs ($1.03 billion/yr.) and unproven effectiveness for preventing infant complications argue against its widespread use. In addition, we now have evidence that bedrest is prescribed at significant physiologic and psychosocial cost to the mother. Pregnant women on hospital bedrest for as little as 11 days (M=29) suffer from debilitating symptoms of muscular (p< .001) and cardiovascular deconditioning, weight loss (p< .01), and depression (p< .001), some of which may not be reversible. Furthermore, upon discharge, previously bedrested women are expected to immediately remobilize and care for self and infant without rehabilitation, thus placing these vulnerable women at further risk for subsequent illness, injury, and parenting difficulties. However, these data came from a small preliminary study. Additional information is needed to confirm and extend these preliminary findings. The aims of this study are to identify the physiologic and psychosocial deconditioning effects of pregnancy bedrest, and to determine whether there is a linear relationship between severity of symptoms and length of hospital bedrest in a larger sample of pregnant women on a continuum of length of hospital bedrest. Subjects will be 168 women who are hospitalized with the diagnosis of preterm labor who are free of other medical conditions. Women will be assessed weekly, from the second or third trimester through six weeks postpartum. A noninvasive hemoglobin/myoglobin spectrophotometer will test muscle deoxygenation response to mild plantar flexion exercise. Other measures include body weight, antepartum and postpartum physical and psychologic symptoms, mobility, stressors of hospitalization, mood changes, and resumption of activities of daily living and functional status after childbirth. Knowledge of the effects of antepartum hospital bedrest is needed to reduce the economic, physiologic, and psychosocial costs of treatment, to provide a basis for interventions to prevent and treat adverse effects, to guide postpartum rehabilitation, and to provide a firm scientific base for use of bedrest therapy for high risk pregnant women.